Sibon

Lotzkat, Sebastian, Hertz, Andreas & Köhler, Gunther, 2012, A new species of Sibon (Squamata: Colubroidea: Dipsadidae) from the Cordillera Central of western Panama, with comments on other species of the genus in the area, Zootaxa 3485, pp. 26-40 : 37

Key to the Lower Central American species of Sibon

1 Seventeen rows of dorsal scales at midbody and 15 rows one head length anterior to cloaca; dorsal scale rows changing orientation from the sides of body towards middorsum................................. Sibon perissostichon ( Fig. 5 E)

- Thirteen or 15 rows of dorsal scales at midbody, usually without reduction on posterior portion of body; dorsal scale rows oriented longitudinally................................................................................. 2

2 Thirteen dorsal rows, both at midbody and one head length anterior to cloaca (very rarely 15 rows at midbody, but then 13 both one head length posterior to head and anterior to cloaca); coral snake-like pattern of alternating light and dark rings................................................................................................ Sibon anthracops

- Fifteen dorsal rows, both at midbody and one head length anterior to cloaca....................................... 3

3 Five supralabials; only one supralabial posterior to orbit, this ultimate one with a higher anterior and a lower posterior portion ( Fig. 2 A); coral snake-like pattern of alternating light and dark rings ( Fig. 1 )......................... Sibon noalamina

- Six or (in most cases) more supralabials, two supralabials posterior to orbit, with the penultimate one greatly enlarged; coloration variable, but no conspicuous coral snake-like pattern of alternating light and dark rings (for example Figs. 5 A–D) 4

4 Enlarged penultimate supralabial usually in contact with eye; dorsal ground color greenish, with an ocellated or blotched rather than a banded or striped pattern; these dark dorsal markings reach at most to outer edges of ventrals, although dark shading or mottling may be present on venter........................................................................ 5

- Enlarged penultimate supralabial usually not in contact with eye; dorsal color pattern banded or striped rather than ocellate or blotched; these dark dorsal markings reach well onto venter or even across venter.................................. 6

5 181–201 ventrals; 112–121 subcaudals; body very slender; head blunt and very distinct from neck; eyes conspicuously large and protuberant.............................................................................. Sibon argus

- 147–173 ventrals; 80–106 subcaudals; body rather stout; snout acuminate, head gradually narrowing towards neck; eyes not conspicuously large, nonprotuberant................................................. Sibon longifrenis ( Fig. 5 C)

6 First infralabials in contact with each other behind the mental.............................. Sibon nebulatus ( Fig. 5 D)

- First infralabials separated from each other by one or two postmentals behind the mental............................. 7

7 Bands dark brown ventrally; laterally, their centers are of a paler brown, which is paler than their borders or the interspaces between the bands; usually a single postmental................................................. Sibon dimidiatus

- Bands dark brown ventrally and laterally, their centers not paler brown than their borders laterally, and darker than interspaces; one or two postmentals present........................................................................... 8

8 Dorsal surface of head with green or yellow as well as red and black markings; ground color of body green; 162–171 ventrals; 77–119 subcaudals........................................................................... Sibon lamari

- Dorsal surface of head with pale and dark brown markings; ground color of body usually olive to pale brown; 161–193 ventrals; 103–135 subcaudals..................................................... Sibon annulatus ( Figs. 5 A–B)

Figures

FIGURE 1. Type series of Sibon noalamina: (A) Holotype (SMF 91539) in life (arrows indicate dorsal rows 3 – 5 next to visible keels), (B) dorsolateral and (C) ventrolateral views of euthanized holotype prior to eversion of hemipenes and preservation, (D) Juvenile paratype (SMF 90180) from type locality in life, (E) juvenile paratype (SMF 89550) from Veraguas in life.

FIGURE 2. Head of Holotype (SMF 91539) of Sibon noalamina: (A) lateral (right side), (B) dorsal, and (C) ventral views. Scale bars equal 1 mm.

FIGURE 5. Snail-eaters collected in western Panama: (A) Sibon annulatus (La Fortuna, SMF 88715), (B) S. annulatus (Río Changena, SMF 91578), (C) S. longifrenis (Cerro Mariposa, SMF 91581), (D) S. nebulatus (La Fortuna, SMF 90209), (E) S. perissostichon (La Fortuna, SMF 88716), (F) and (G) Dipsas articulata (Cerro Negro, SMF 89952), (H) D. temporalis (Cerro Negro, SMF 89769).